EP0533133A1

EP0533133A1 - Cooling method of continuous casting and its mold

Info

Publication number: EP0533133A1
Application number: EP92115835A
Authority: EP
Inventors: Norio Ohatake; Makoto Arase; Yoshitaka Nagai
Original assignee: YKK Corp; Yoshida Kogyo KK
Current assignee: YKK Corp
Priority date: 1991-09-19
Filing date: 1992-09-16
Publication date: 1993-03-24
Anticipated expiration: 2012-09-16
Also published as: AU656404B2; DE69227967T2; ATE174827T1; JPH0577011A; AU2206792A; NO923648L; FI98795B; CA2077310C; NO923648D0; DE69227967D1; US5452756A; FI924156A; FI924156A0; JP2721281B2; CA2077310A1; FI98795C; EP0533133B1; NO302689B1

Abstract

A cooling method and a cooling mold in a continuous casting wherein even if a continuous casting rate is increased, a proper cooling is carriedout to prevent a danger of a breakout, so as to improve the stability of casting and the high quality of an ingot (4).

A cooling mold comprises water cooling jackets (21, 22) which are provided in the inner part of the mold (2), a first cooling water jetting mouth (23) which is arranged at a distance of 20 to 45 mm between a contact position of a primary cooling water and an other contact position of a secondary cooling water on the ingot (2).

By use of the cooling mold (2) wherein a primary and a secondary cooling water impinging angles are respectively set at 15 to 30 degrees and at 30 to 60 degrees, the primary cooling water is impinged from the first cooling water jetting mouth (23) to a molten metal (3) which is cooled with the inner surface of the cooling mold (2) to carry-out a primary cooling, and nextly, the secondary cooling water is impinged from the second cooling water jetting mouth (24) to initial zones of a transition boiling zone and a film boiling zone which are produced with the impingement of the primary cooling water, so that a vapor film generated in the transition boiling zoneand the film boiling zone is broken out to provoke a nucleate boiling so as to carry out a direct se condary cooling with the secondary cooling water.

Description

BACKGROUND OF THE INVENTION

Field of the Invention;

This invention relates to a cooling method and a mold in a continuous casting for casting ingots from molten aluminum, aluminum alloys, or othermetals.

Description of the Related Art;

In this continuous casting method as shown generally in FIG.4, a molten metal 13 is injected into a mold 12 which is water cooled from a tandish 11 through an orifice plate 15, so that the molten metal is cooled in the mold 12 to cast an ingot 14. The molten metal 13 which is introduced from the orifice plate 15 to the mold 12, is contacted with the wall surface of the mold 12 to form a thin solidified shell and is further cooled and cast with a cooling water which is impinged from the mold 12.
In the continuous casting, a higher rate casting is desired to improve the production and it is required to realize the higher rate casting and simultaneously to promote the casting quality due to high cooling.
In the high rate casting, in order to form the solidified shell in the mold for solidifying the molten metal, it is required to extract a more amount of heat and thereby to increase the amount of a cooling water. The cooling water which is impinged from the mold, is applied to and cooled the ingot of high temperature directly. However, when the casting rate is increased, since the surface temperature of the ingot becomes higher in a cooling water impinging position, the ingot surface produces a transition boiling zone and a film boiling zone and there exists a vapor film which is adiabatic phase between the ingot surface and the cooling water. Then, even if the amount of the cooling water is increased, the cooling water does not effectively function because of a heat extraction to increase a danger of a breakout, and to generate problems so as to cause quality defects of the ingot. Hence, these problems have been factors for considerably reducing the casting stability and the quality stability.
In order to dissolve these problems, there are cooling methods for directly impinging a cooling water at two steps as disclosed for example in JP,A Sho 58-212849 (Japanese Patent Publication of Unexamined Application).
However, in the two steps cooling method with the cooling water which is disclosed in the above Japanese Patent Publication, since a distance between a first cooling zone and a second cooling zone becomes considerably long, that is half to two times diameter of the ingot, the surface temperature of the ingot cooled in the first cooling zone is again heated in the second cooling zone with heat flow from internal region of the ingot. Hence, even if the second cooling is carried out, the transition boiling and film boiling phenomenonna are again produced to reduce the cooling efficiency. According to the high rate casting, this tendency is more increased to reduce the cooling efficiency considerably.

SUMMARY OF THE INVENTION

It is therefore an object of this invention to provide a method for cooling an ingot in a continuous casting wherein even if a continuous casting rate is increased, a proper cooling may be carried out to prevent a danger of a breakout so as to provide a stable casting and a high quality of an ingot.
This invention is characterized in that a cooling method in a continuous casting for continuously withdrawing and casting an ingot from a cooling mold while cooling a molten metal in the mold comprises a primary chill step for impinging a primary cooling water from the cooling mold to the molten metal which is cooled in the cooling mold, and a secondary chill step for impinging a secondary cooling water to initial zones of a transition boiling zone and a film boiling zone which are established with the primary cooling water impingement, so that a vapor film generated in the zones is broken out to provoke nucleate boiling.
This invention is preferably characterized in that a primary cooling water impinging angle against an ingot surface is 15 to 30 degrees and a secondary cooling water impinging angle against the ingot surface is 30 to 60 degrees. When the ingot has a diameter of 6 to 9 inches, an ingot contact position of a primary cooling water impinged from the mold is disposed at a distance L1 of 15 mm to 40 mm from a meniscus, and a distance L2 between the ingot contact position of the primary cooling water impinged from the mold and the other ingot contact position of the secondary cooling water impinged to the transition boiling zone and the film boiling zone is preferably 20 mm to 45 mm.
A cooling mold for accomplishing this cooling method comprises water cooling jackets in an inner part thereof, and a primary cooling water jetting mouth and a secondary cooling water jetting mouth which are disposed at the predetermined distance in the withdrawing direction of an ingot, wherein theprimary cooling water jetting mouth is set at an angle of 15 to 30 degrees against the ingot surface and the secondary cooling water jetting mouth is set at an angle of 30 to 60 degrees against the ingot surface. The primary cooling water jetting mouth has preferably a whole peripheral slit shape and the secondary cooling water jetting mouth has also a grooved or holed shape.
This invention will be illustrated in detail with the operation;
Generally in a casting mold, when a cooling water is impinged directly to a high temperature ingot to cool it, vapor bubbles or vapor films are produced on the high tempature ingot, so that the cooling water contacting with the ingot extracts heat from the ingot surface of high temperature.
However, even when the cooling water is impinged to a high temperature ingot of about 600°C to promote a forced convection heat transfer, the transition boiling zone and the film boiling zone are produced immidiately after the cooling water is contacted with the high temperature ingot, so that they are coated with a vapor film so as not to contact the cooling water with the ingot surface. In order to prevent the vapor film, even if the amount of the cooling water is increased to improve the cooling effects, there is a limit in this cooling effects, and at the same time, even if the pressure of the cooling water is increased, there is also a limit in the improvement of the cooling efficiency.
On one hand, the length of a non-solidified part of the ingot in the casting process depends on a considerably high correlation with a cooling water amount, a cooling position and an ingot surface temperature. The shorter length of the non-solidified ingot part prevents the more casting cracks and the weaker cooling causes the longer length of the non-solidified ingot part, so that the extent of the solid-liquid coexitence phase is spread to increase the danger of the casting cracks.
This invention is intended under the causality of these phenomenonna to produce a firm solidified shell by newly impinging a cooling water to a transition boiling zone and a film boiling zone to break out a continuous vapor film produced thereon with the pressure of the cooling water, and to cool the ingot surface with a direct cooling water to generate a nucleate boiling so as to provide an efficient cooling, without compensating with the increase of the amuont and pressure of the cooling water for the reduction of the cooling efficiency in the transition boiling zone and the film boiling zone which are produced on the ingot surface of high temperature.
In a casting of an ingot having a large diameter of 6 to 9 inches, a position contacting a primary cooling water impingement with a high temperature ingot is disposed at a distance L1 of preferably 15 to 40 mm from a meniscus. When the distance L1 is less than 15 mm, the danger of generating the breakout in the start of the casting and the breakout due to slight changes of casting conditions during casting is increased. When the distance L1 exceeds 40 mm, the direct cooling with the cooling water is retarded to cause surface defects such as bleeding out and external cracks of the ingot surface. The depth of an inverse segregation layer becomes deep to generate quality defects.
It is also favourable to set a distance L2 of 20 to 45 mm between the position for contacting the primary cooling water with the ingot and the other position for contacting the secondary cooling water with the ingot. When the distance L2 exceeds 45 mm, the cooling is retarded to lengthen the non-solidified length within the ingot so as to increase the danger of the cast cracks.
The cooling water impinging angle against the ingot surface is one of the important factors in the efficient casting. It is favourable to set a primary cooling water impinging angle at 15 to 30 degrees and a secondary cooling water impinging angle at 30 to 60 degrees. When the primary cooling water impinging angle is set at less than 15 degrees, the distance from the meniscus is increased to cause the bleeding out, and when it is set at more than 30 degrees, the cooling water flows inversely at the start of the casting to cause the breakout. It is required to set the secondary cooling water impinging angle at 30 to 60 degrees so as to break out the vapor film which is generated in the transition boiling zone and the film boiling zone of the primary cooling water.
With respect to the shape of a cooling water jetting mouth which is formed in a cooling mold, the whole periphery of the mold is provided with a slit, groove, or hole type opening. The primary cooling water jetting mouth adapts the slit-shaped opening on the whole inner circumferential surface of the mold to cool uniformly the whole outer periphery of the ingot. The secondary cooling water jetting mouth adapts the grooved or holed opening on the whole periphery of the mold to break out the vapor film which is produced in the transition boiling zone and the film boiling zone.
Further features and advantages of the invention will be apparent from the detailed description below, together with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal sectional view of an important part which shows a cooling state of a continuous casting according to this invention ;
FIG. 2 is a longitudinal sectional view of an important part which shows a starting state of the casting ;
FIG. 3 is a partial enlarged view of FIG. 1 ; and
FIG. 4 is a longitudinal sectional view of an important part which shows a cooling state in the conventional continuous casting.

DETAILED DESCRIPTION

A preferred embodiment of this invention will be essentially illustrated with reference to the accompanying drawings. This invention is not only adopted in a horizontal casting which is illustrated herein, but also may be adopted in a vertical casting. FIG. 1 is a longitudinal sectional view of a cooling portion in the casting, which is a typical embodiment of this invention, FIG. 2 is a longitudinal sectional view for showing the cooling portion at the start of the casting, and FIG. 3 is a partially enlarged sectional view of the cooling portion.
In these drawings, a tandish, a molten metal, an orifice plate, an orifice, a starting block, and a starting pin are respectively indicated with 1, 3, 5, 6, 7, and 8. These members have essentially the same structure as the conventional casting members.
A cooling mold which is disclosed as the feature part of this invention, is indicated with 2. First and second ring water cooling jackets 21, 22 are formed in front and rear positions at a predetermined space on the same axis of the cooling mold. A part of each water cooling jacket 21, 22 is communicated with an external cooling water supply pipe. The first and second water cooling jackets are respectively opened on the inner surface of the cooling mold 2 to form individual jet mouth 23, 24. The jet mouth 23 of the first water cooling jacket 21 which is arranged near the tandish 1, is formed with a slit opening on the whole inner circumferential surface of the mold 2. The jet mouth 24 of the second water cooling jacket 22 which is arranged far from the tandish 1, is formed with a grooved or holed opening on the whole inner circumferential surface of the mold 2.
A set position of the jet mouth 23 of the first water cooling jacket 21 is determined by a position for contacting a cooling water jetted from the jet mouth 23 with the ingot 4. In the ingot diameter of 6 to 9 inches, the contact position is favourably disposed in the extent L1 of 15 to 40 mm to set the jet mouth at the distance L1 from the meniscus.
A set position of the mouth 24 of the second water cooling jacket 22 is also determine by the distance L2 between the position for contacting the primary cooling water with the ingot 4 and the other position for contacting the secondary cooling water with the ingot 4. In the ingot diameter of 6 to9 inches, the distance L2 is favourable in the extent from 20 to 45 mm.
Moreover, commonly in the first and second water cooling jackets 21 and 22, the cooling water impinging angle against the ingot surface exerts a large influence upon the cooling efficiency. In accordance with this invention, the angle formed between the impinging cooling water and the ingot surface is preferably set at 15 to 30 degrees in the primary cooling water and at 30 to 60 degrees in the secondary cooling water.
In the continuous casting with the above-mentioned structure, a starting block 7 is inserted into a cooling mold 2 of this invention in the casting start as shown in FIG. 2. A starting pin 8 secured to the tip of the ingot is contacted with an end face of an orifice plate 5. In this state, a molten metal is introduced through orifices 6 of the orifice plate 5 into the mold 2, and when the starting block 7 is withdrawn at a predetermined rate from the mold 2, the casting is started.
Plural orifices 6 are formed in the orifice plate 5. The molten metal 3 in the tandish 1 is introduced through the orifices 6 into the cooling mold 2, and since the molten metal 3 is contacted with the inner surface of the mold 2, the surface of the molten metal is cooled to produce a thin solidified shell. Then, the molten metal is direct-cooled with a primary cooling water which is jetted from the first jet mouth 23 of the mould 2, so as to progress the solidification. So, since a transition boiling zone and a film boiling zone are produced on the surface of the ingot 4 with the impingement of the primary cooling water, when a secondary cooling water is impinged from the second jet mouth 24 of the cooling mold 2 toward the vapor film of these zones, the transition boiling zone and the film boiling zone are broken out with the impinging cooling water to provoke a nucleate boiling, so as to produce a firmer solidified shell with the secondary cooling directly against the ingot surfaces.

This invention is illustrated in the embodied example wherein an ingot of an aluminum alloy based on Japanese Industrial Standard 6063 is cast by use of a casting apparatus shown in FIG. 1 in the following casting conditions.
( 1 ) The distance L1 between the meniscus and the contact position of the primary jet cooling water is variously changed in the following casting conditions to cast the ingot. The results are shown in a Table 1.

a. Kinds of alloy	JIS 6063 aluminum alloy
b. Diameter of ingot	7 inches ( 178 mm )
c. Casting rate	350 mm / min
d. Casting temperature	690 c
e. Amount of primary jet cooling water	85 l / min

Table 1

L 1	Breakout	Bleeding out; Inverse segratation
10 mm	exist	-
15 mm	not existed	fine
25 mm	not existed	fine
35 mm	not existed	fine
40 mm	not existed	a little
45 mm	not existed	much

( 2 ) The distance L2 between contact positions on the ingot of the first and second impinging cooling water is variously changed in the following casting conditions to cast the ingot. The results are shown in a Table 2.

a. Kind of alloy	JIS 6063 aluminum alloy
b. Diameter of ingot	7 inches
c. Casting rate	350 mm / min
d. Casting temperature	690 c
e. Amount of primary jet cooling water	85 l / min
f. Amount of secondary jet cooling water	45 l / min
g. Distance between meniscus and contact position of primary impinging cooling water	25 mm

Table 2

L 2	Nucleate boiling effects	Casting cracks
15 mm	small	a little
20 mm	middle	not existed
30 mm	large	not existed
40 mm	large	not existed
45 mm	large	a little
50 mm	middle	a little

As stated hereinabove, in accordance with this invention, advantageous results may be obtained as follows ;

1. Since a slight distance from a meniscus produces a firm solidified shell, it is possible to provide a stable high rate casting so as to improveproduction and yield considerably.
2. Since it is possible to provide effective cooling, an amount of a cooling water is considerably reduced to miniaturize a cooling water pumping equipment and to save an energy.
3. Since a powerful cooling is carried out at the slight distance from the meniscus, it is possible to prevent surface defects such as bleeding out and the like.
4. Since the powerful cooling is carried out in two steps, only a short non-solidified portion is produced in the ingot to prevent internal defects such as casting cracks and the like.
5. Since an internal composition of the ingot becomes fine with the powerful cooling, it is intended to shorten a homogenizing process time, to promote an easy extrusion and to improve a strength of an extruding material.

It is to be understood that the invention is not limited to the features and an embodiment hereinabove specifically set forth but may be carried out in other ways without departure from its spirit.

Claims

In a continuous casting for continuously withdrawing and casting an ingot (4) from a mold (2) while cooling a molten metal (3) in said mold (2); a cooling method comprising a primary chill step of impinging a primary cooling water from said mold (2) to said molten metal (3) which is cooled in said mold (2), and a secondary chill step of impinging a secondary cooling water to initial zones of a transition boiling zone and a film boiling zone which are generated with the primary cooling water impingement, so that a vapor film generated in the zones is broken out to provoke a nucleate boiling.
A cooling method according to claim 1, wherein a primary cooling water impinging angle against an ingot surface is 15 to 30 degrees, and a secondary cooling water impinging angle against said ingot surface is 30 to 60 degrees.
A cooling method according to claim 1, wherein said ingot (4) has a diameter of 6 to 9 inches, and an contact position of a primary cooling water impinged from said mold (2) is set at a distance L1 of 15 to 40 mm from a meniscus.
A cooling method according to claim 1, wherein said ingot (4) has a diameter of 6 to 9 inches, and a distance L2 between said ingot contact position of the primary cooling water impinged from said mold (2) and an other ingot contact position of said secondary cooling water impinged to said transition boiling zone and said film boiling zone is 20 to 45 mm.
A continuous casting mold for continuously withdrawing and casting an ingot (2) from said mold (2) while cooling a molten metal (3) in said mold (2) comprising water cooling jackets (21, 22) which are provided in the inner part of said mold (2), and a primary cooling water jetting mouth (23) and a secondary cooling water jetting mouth (24) which are disposed at a predetermined distance in the withdrawing direction of said ingot (4).
A continuous casting mold according to claim 5, wherein an angle of said primary cooling water jetting mouth (23) against said ingot surface is 15 to 30 degrees and an other angle of said secondary cooling water jetting mouth (24) against said ingot surface is 30 to 60 degrees.
A continuous casting mold according to claim 5, wherein said primary cooling water jetting mouth (23) provides a slit shape on the whole inner circumferential surface thereof, and said secondary cooling water jetting mouth (24) provides a grooved or holed shape.